DESCRIPTION OF THE PRIOR ART
Since poly(alkylene terephthalates) are generally of insufficient impact strength for molding purposes, there have been many attempts to improve the impact strength. U.S. Pat. No. 3,578,729 shows use of .alpha.-olefin/acrylic ester copolymers; U.S. Pat. No. 3,769,620 shows terminally carboxylated .alpha.-olefin polymers such as carboxylated polyethylene for impact strength improvement; U.S. Pat. No. 3,839,499 show isotatic polybutylene-1 for this purpose; U.S. Pat. No. 3,405,198 shows polyethylene as an impact modifier; U.S. Pat. No. 3,435,093 shows ethylene/methacrylic acid; U.S. Pat. No. 3,591,659 shows polyalkyl acrylates, methacrylates, or ethacrylates for this purpose; U.S. Pat. No. 3,723,574 shows polystyrene/butadiene diols; U.S. Pat. No. 3,787,530 shows styrene/acrylonitrile; U.S. Pat. No. 3,864,428 shows ABS and MBS rubbers in combination with polycarbonate for impact modification; British Pat. No. 996,621 and U.S. Pat. Nos. 3,869,427 and 3,583,935 show reduction of free carboxyl groups in polyesters by reaction with epoxy monomers; U.S. Pat. No. 3,553,157 shows polyfunctional compounds as chain extending agents for poly(alkylene terephthalates); British Pat. No. 1,208,585 shows such a polyfunctional compound to chain extend poly(ethylene terephthalate) with the further inclusion of a rubbery impact modifier which optionally includes reactive groups such as epoxy groups which react with the polyfunctional compound so as to become grafted to the polyethylene terephthalate through the polyfunctional compound. Except for the last-mentioned patent, I am not presently aware of any prior suggestion of reactive impact modifiers for poly(alkylene terephthalates). It appears that prior workers have taken two different approaches to the problems of impact strength improvement and melt strength improvement, using separate additives to solve each problem. For example, U.S. Pat. No. 3,368,995 shows improvement of melt viscosity of poly(ethylene terephthalate) by inclusion of fiber reinforcement.
The melt viscosity and hot melt strength of highly crystalline polyesters, such as film and fiber grade poly(ethylene terephthalate), are too low to permit profile extrusion and blow molding operations. Polyester film is produced by extrusion onto chilled drums and subsequently biaxially stretch oriented at temperatures above the second order transition temperature. Very high molecular weight polyesters are required for blowing bottles. The melt viscosity of film and fiber grade poly(ethylene terephthalate) is so low that horizontal extruders can only be employed when a right angle adaptor is employed for the extrudate. Normally vertical extruders are employed.